This invention relates to a method and system for detecting reverse rotation of a compressor due to improper wiring.
Compressors are a major component in air conditioning and refrigeration systems. One popular type of compressors is a scroll compressor. In a scroll compressor, a pair of wraps interfit to define a plurality of compression chambers. One of the wraps is driven through an orbit relative to the other, and the compression chambers are reduced in volume such that they compress an entrapped fluid. Scroll compressors are designed to rotate in a forward direction for fluid compression. They are not intended to rotate in the reverse direction during normal operation.
However, if the compressor is improperly wired, or under certain operational conditions, it is possible for the compressor to operate in reverse. Scroll compressors include a motor received in a sealed compressor shell. The refrigerant leading into the compression chambers passes over the motor on its way to the compressor, cooling the motor.
During reverse rotation, little or no refrigerant is pumped through the compressor, and thus the motor can quickly overheat. At the same time, refrigerant is not driven through the compression chambers. Thus the pair of interfitting scroll wraps can also quickly overheat due to heat generated by internal friction between the fixed and orbiting wrap. If reverse rotation is permitted to continue for a long period of time, there is the possibility of damage to the scroll compressor wraps or the motor.
The prior art placed motor protection sensors or line breaks, which would cut off power to the compressor if the motor is overheated. However, this can result in continuous compressor cycling as the motor cools off and compression comes back on line. Then the motor overheats again and the compressor is cycled off.
This of course prevents the compressor from performing its duty of compressing refrigerant, and can lead to potential compressor damage due to continuous cycling. Also the compressor wraps can be damaged due to overheating before the compressor is cycled off.
For residential or commercial applications, it is sometimes possible to detect reverse rotation since it typically results in loud undesirable noise. Since the compressor in a residential or commercial application is typically near occupants, the sound may be noted and corrective measures can take place. However, in typical container refrigeration applications, such as refrigerated transport containers, the compressor and refrigerant system are not mounted near any operator who could hear the sound. Further, such systems include large fans which also generate substantial noise. This noise often masks any increase in the compressor noise.
A three phase compressor is driven by a motor receiving three phase power. Such a compressor can run in reverse, if the connections are miswired at the main power supply or at the connection to the compressor.
The problem of miswiring is especially acute if the connections must be repeatedly made. This is particularly true with three phase compressors in transport container refrigeration where electrical reconnections are frequently made thus increasing the risks of miswiring.
The present invention discloses methods and apparatus for detecting and responding to the detection of compressors running in reverse.